It is well known that control of the arc voltage (and thus knowledge of the arc voltage) is helpful to ensure a high quality weld. (As used herein arc voltage refers to the voltage between the electrode and the workpiece.) Prior art commercial welding systems have typically sensed the voltage at the power source or at the wire feeder, and have used this voltage as a proxy for the actual arc voltage between the welding electrode and the workpiece. By doing so, all voltage drops along the weld cable (due to intrinsic resistance and intrinsic inductance) are ignored. This type of voltage sensing was the best that could practically be achieved in the prior art, and prior art control schemes were forced to make do with this inaccurate voltage sensing. However, advanced control schemes benefit from more accurate arc voltage feedback: Voltage drops due to intrinsic line inductance and resistance should not be ignored. One such advanced control scheme is described in U.S. patent application Ser. No. 09/024,944, Method and Apparatus For Short Arc Welding, filed Feb. 17, 1998, which was invented by the present inventors, and owned by the present assignee, and which is hereby incorporated by reference. Accordingly, the inaccurate prior art voltage sensing techniques need improvement.
Non-commercial prior art welding systems have used a separate arc voltage sense wire that was clipped to a point near the welding electrode to more accurately measure the arc voltage. The use of a separate sensing lead is problematic in that it adds another loose wire to the welding system which can get in the way of the operator, potentially damaging the sense lead itself. Another problem with the prior art method is that it is only temporarily attached near the welding electrode and therefore can easily become unattached during the welding operation. Thus, the non-commercial separate lead is not useful (and has not been employed) in commercial applications. Prior art commercial systems use a similar work piece sense lead, that is clipped to the work piece. This type of clip-on work piece sense lead suffers from the same problems as a clipped on electrode sense lead.
Another prior art sense lead is used with a pull-type wire feeder. Such a wire feeder has a motor at the torch end of the weld cable that pulls the wire to the torch. Because a wire feed motor (including power and control leads) is located at the torch, the voltage was sensed there. However, the design is not useful for systems that have the wire feed motor located remotely from the torch.
Accordingly, it is desirable in the art to provide an arc voltage sense lead that does not add an extra loose wire to the welding apparatus. Preferably, such a sense lead is permanently attached. Also, such a sense lead is preferably attached near the welding arc, to more accurately and reliably sense the arc voltage, and is useful with wire feeders where the torch is not located near the wire feed motor.